Sized paper, composition therefor, and method of making same



Patented Apr; 17, 1951 UNITED' STATES PATENT OFFICE SIZED PAPER, COMPOSITION THEREFOR,

AND METHOD OF MAKING SAME T 'Paul B. Davidson, Wilkinsburg, Pa., assignor to Strathmore Paper Company, Springfield,Mass., a corporation of Massachusetts No Drawing. Application March 21, 1949, Serial No. 82,702

paper is excellently adapted to the demands made,

upon papers which require a treatment in the wet condition or may be subjected to wetting while in service; such as blueprint papers.

One feature of the invention is the provision of a sizing liquor capable of inducing high wet strengths in paper.

Another feature of the invention is the'prdvision of a paper having wet tensile strength in excess of 900 grams and wet rub value above 5.

Another feature of the; invention is the provision of a paper having the stated strength values and being dimension-fast, that is, being highly resistant to change of dimensions as a result of prior wetting.

A further feature is the production of a paper having the stated wet strength values, satisfactory dry strength values, and satisfactory resistance to the penetration and spreading of liquids applied to the paper such as writing and printing inks, and light-sensitive coatings.

A further feature of the invention is a process of producing such a paper by reacting papermakers sizing starch with glyoxal in the presence of the paper fibers.

A further feature is a process of producing such a material by employment of existing papermaking machines, through use of an improved sizing liquor, with a completion of the procedure during the normal drying procedure.

With these and other features in view, asiwill.

appear in the courseof the following description and claims, illustrative examples of .practice are set forth for indicating the properties ofthe paper produced and the procedure of making the;

same.

These examples will be set out illustratively withthe employment of a basic stockorpaper material which is presently accepted in the industry as being adapted for blue-print paper. By way of comparison, when this stock was tubsized in the usual way with a 10 per cent dispersion of an oxidized or chlorinated starch, designed for this type of sizing, and then dried by heating, the wet tensile strength was about 460 grams.

By way of further comparison, when samples of According to this invention, a size for samples of this paper was prepared by cooking the starch with glyoxal per cent of the dry weight of the starch) this was applied in the same manner as the formaldehyde-treated or un-treated starch;

' and then subjected to drying and heating, whereupon it was found that the wet tensile strength was 1160 grams. On another lot of paper, treated in the same way, the increase in wet tensile strength was from 450 grams for the starch-sized paper to 1340 grams for the starch-glyoxal-sized paper.

In addition to this great increase of wet tensile strength, it was discovered that the resistance to wet abrasion, or the so-called wet-rub value, was greatly increased. For comparison, the starchsized paper gave a value of 2 rubs, the starchfomaldehyde-sized paper gave a wet rub of 2, while the starch-glyoxal-sized paper gave a wet rub of 17.

The testing methods employed were modifications of the TAPPI standards but are believed more severe. Wet tensile strength was determined by T-456M44, but immersing the whole paper strip in water at 21 C. for a half-hour, and then'mounting the wet strip in the jaws of the standard strength tester, and making the test as prescribed for dry tensile strength, by T-lOl-M- 44. Wet rub testing consisted of soaking pieces of the paper in water at 21 C. for one minute, and then rubbing with the thumb until roughness is felt to have been developed on the surface of the paper.

The dry tensile strength is not decreased by the treatment, and in most cases is improved with other dry properties.

In these comparisons, the starch sizings were prepared by suspending 1200 grams of the oxidized or chlorinated starch in 4800 ml. of water, and dispersing the starch by cooking for ten minutes at between C. and C. The system was then diluted to 12 liters with water, therewith cooling to a temperature of about 40 degrees to 45 degrees 0., and used in a pilot plant having a sizing press which accommodates rolls of paper twelve inches wide and about eleven inches in diameter. The speed of this sizing press was adjusted so that the degree of sizing (as measured by the amount of wet size dispersion soaked up by the paper) was the same as that produced on commercial machines during commercial runs.

In preparing the starch-formaldehyde or starch-glyoxal sizes, the starch was suspended and dispersed as before but, after dispersion, the formaldehyde or glyoxal was added, and the cooking continued for an additional five minutes beas before.

7 the original starch must have been treated in such a manner that, when cooked at above the gelation temperature of the starch, that is to say,

at a temperature of between. about 70 C, and 80? C., the modified or solubilized'starch must have It has been found that the concentration of glyoxal, for sizing blueprint papers to obtain high wet tensile strength and wet rub values, depends upon the efiective starch concentration in lost its identity of granules and also be capable of producing a fluid or free flowing (Saybolt viscosity below 40 seconds) sizing dispersion at the temperatures normally maintained for the sizing operation, i. e. between 40 C. and 60 C. (104-140 degrees F.). dispersion is required so as to allow the material to soak into the paper and'permit the excess to be removed from the surface by squeeze rolls while leaving the paper essentially with its orig inal surface characteristics. The general molecular starch structure does not appear changed: and the herein-described glyoxal reaction occurs with the various modified forms. Such treatment of the raw starch to produce a fluidly dispersable material is accomplished in practice by one of several procedures, for example, by a chlorination 'or oxidizing operation, by dextrinization, by enzyme conversion, etc. Such procedures of preparing satisfactory fluid dispersions of starch are described, for example, in fPaper Trade Journal for February 19, 1942, at page 107 et seq., for February 17, 1938, at page 2'7 et seq. and for December 3, 1942, at page 30 et seq. It will be understood that the Words starch dispersion refer to a starch size, of components used by paper-makers for surface or tub sizing operations, present in the form of free flowing aqueous dispersion: and that papermakers modified starch is employed in its normal meaning of a starch converted for papermakers use and capable of forming a fluid dispersion as distinguished from a jelly or paste or suspension of separate particles.

It has been found that glyoxal reacts with these various so-called modified starches in substantially the same fashion. For example, Table I shows the behavior with diastase-converted starch and with chlorinated starch, the starch being present at 10 per cent (dry weight) concentration in the sizing liquor in each case.

Similar results have been obtained with starch which has been slightly dextrinized by roasting, as referred to in the aforesaid publications:

Table II Wet Wet Rub Tensile 10% dextrin size 2 700 10g, dextrinsize+1 6% glyoxa1 3 790 10 a'dextrin size+4.8% g1yoxa1 9 l, 010

This free flowing property of the the liquor. Assuming a 10 percent (dry weight) starch concentration, as a standard, a concentration of less than 2 per cent of glyoxal produces a greater increase of values than can be obtained with'formaldehydaior example, but does not produce the high and optimum values which are desirable'for blueprint papers. On the other hand,

- a concentration ofmore than 5 per cent of glyoxal in such liquors leaves the paper with so much unchanged glyoxal that a reducing environment results: so that the reducing effects, in the presence of the photographic blueprint and negative sensitizing coatings, tend to cause a premature change of color, for example, what is called.

silvering. This difiiculty is not present, however, when the paper'is to be used for printing. Thus, the desirable range of concentration of glyoxal, for a 10 per cent starch solution, is between 0.2 per cent and 0.5 per cent, or from onefiftieth to one-twentieth of the concentration of the starch itself for. photographic papers. At these values, the following wet strengths can be expected:

While it has been found that a 10 per cent concentration of starch in the sizing liquor is a desirable one, changes of this ratio of dispersion can be used, for specific cases. It has been found that if the starch dispersion is too dilute (say 5 per cent or less concentration of starch in the system) then there is a lesser reaction between.

the glycxal and the starch, and lesser strength values develop. The commercial preparation of a surface or tub-size comprises the dispersion of about 15 to 35 per cent of modified starch in the original water, by cooking, and then dilution of the'same to a proper viscosity for application on the commercial machine. When the glyoxal is cooked into the starch, at such concentrations the particular percentage of starch present appears to have no appreciable effect upon the'wet tensile strength, and only a slight effect upon the wet abrasion or wet rub value. By way of comparison, employing a bond paper, rather than a blueprint paper, the following values were obtained with difierent starch concentrations:

" For Tablesil and II, identical papers were usedi for tub-sizing, being Strathmore blueprint paper #6386.

' Likewise, the time of teenager the starch and glyoxal does not appreciably change. the 'wet strength developed in the paper. For example,

after the cooking for dispersion had been completed, an additional cooking time in th presence of glyoxal, of five minutes, gave a wet tensile strength of 1440 grams, while cooking for ten minutes gave 1320 grams, and for fifteen minutes gave 1350 grams. That is, other factors appear to have a greater influence, including minor variations in the preliminary cooking for dispersion: but in each of these instances of timing, it will be noted that the final wet tensile strength was above 1300 grams. Indeed, it is believed that the major part of the strength is developed during the final drying and heating operation, and that the preliminary coupling, or like reaction, occurring in the preparation of the sizing solution, is relatively lesser in importance. Thus, the cooking occurring while the glyoxal is being distributed in the dispersed starch, within a couple minutes, may be sufficient in some instances for developing adequate strengths.

, In practice, it has been found to make little difference in the final strength properties, whether the glyoxal is added to the water before the starch is suspended therein and the cooking started, or whether the glyoxal is added after the starch has been dispersed in the water by cooking or the like. In the previous tables, the size solution was prepared by adding the glyoxal after the dispersion had been accomplished by cooking. For purpose of comparison, sizing solutions were prepared by adding the selected quantity of technical or commercial glyoxal to liters of water, adding preservative at the same time when preservative is to be used. 1200 grams of the modified starch was then added slowly, with stirring to obtain an even suspension. The'systern was then heated to above the gelation point of the starch (between 70" C. and 75 C.) a temperature of 80 to 785 being preferably employed: the cooking is carried on at this temperature for between five and ten minutes. The heating can be done by the direct injection of live steam, or by use of a steam-jacketed kettle. The direct injection is preferred, to avoid possible formation. of a layer of gelled and less soluble starch material on the hot surface of the kettle. Comparing the results, dependent upon the time of adding the glyoxal:

Table V Wet tensile Glyoxal added after starch is swelled 1300 Glyoxal added after starch is swelled 1240 Glyoxal added before starch is swelled 1170 Glyoxal added before starch is swelled 1250 Glyoxal added before starch is swelled 1230 However, when raw starch is to be dispersed by the enzyme conversion method, the glyoxal must be added after the starch has been dispersed from its suspension form, in order to avoid the action of glyoxal in killing the enzyme. Since a normal procedure is to permit the conversion to proceed to a desired point of viscosity or dispersability of the starch, and then to terminate the conversion by heating, the glyoxal can properly be added just before this heating is begun.

The reaction between glyoxal and the starch, which is believed to occur, takes place in sizing solutions of normal acidity: and will also occur in the presence of 'weak alkaline salts. Owing to the possibility of an auto-oxidation-reduction reaction of the Cannizzaro type, when strong alkali conditions are present, the solution should not be more alkaline than about pH 9.0. However, the presence of weak alkaline salts such as lithium and sodium carbonates do not cause this reaction to take place to any appreciable degree, nor do these salts change the reactivity of glyoxal toward modified starches in any fashion to impair the wet tensile strength of the sized paper produced thereby.

The glyoxal may be of high chemical purity, but such is not needed: in practice it can be employed in the commercial form, sometimes called a polymer and at times designated as tetrahydroxydioxan. The material used for several of the above examples had a concentration of 30 per cent; but commercial products may vary from this by several per cent, due allowance being made in the amount of material taken.

The technical grade of glyoxal contains an appreciable concentration of formic acid, and exhibits a value of pH 1.3 to pH 2.0. When it is desired to operate under more alkaline conditions, this acid can be neutralized or partly neutralized with such weak alkalies as the lithium carbonate or sodium carbonate stated above, and the resulting glyoxal solution can then be added to the starch dispersion with essentially the same results as though the original glyoxal, without neutralization, had been employed. some buffering appears to be present from the starch dispersion, but in general the wet rub resistance appears greater when glyoxal solutions, and prepared sizes, are used with a pH above 5.0, as for example:

In preparing the sizes used for Table VI, the starch dispersion was brought to the stated pH value of 7.1 in the third example above, before adding the neutralized glyoxal solution. The results of Table VI were obtained by using specimens from the same lot of paper; except fo the first example above, which employed a paper having a somewhat less et tensile strength in the absence of the glyoXal-starch sizing.

The results of Table VI were obtained by use of chlorinated starch, which when dispersed exhibited a pH of 5.75.

In another series of sizings, using 4 per cent of glyoxal, and adjusting its pH value as noted, results were obtained:

In preparing and testing sizing liquors within the presently preferred pH values of about 4 to 6 7 for the sizing solution, it was found that the following variations may be expected:

Table VIII Approximate Wet pH of size Tensile Avewge It has been found that excellent conditions can be produced by employing the sizing solution in V a size press formed as a part of a normal papermaking machine. Thus, the paper web is introduced to the sizing solution and is permitted to take up a quantity of the sizing solution which is dependent upon the properties of this sizing liquor, the time of contact, the preliminary condition of the paper stock, etc. Thereafter the water is evaporated away, and then the sized paper is dried.

The temperature at which the sized paper is dried, and therewith apparently a final reaction produced, has some effect upon the final wet strength developed. The temperatures available in a commercial paper-making machine are determined by the practical necessities of obtaining a good rate of production, and by limitations of steam pressure to be employed in the drying drums on the machine. It has been found that temperatures of 121 C. to 134 C. are easily maintainable on the machine which has been used for the work. The drying temperature should be from 110 C.to 150 C.,to secure a sufiicientlyrapid drying and reaction, and to avoid side reaction. In practice, for example, the following values were found, under otherwise identical conditions:

Since the drying time on a paper-making machine may be a critical commercial factor, it is interesting that the actual. drying time at a given temperature is not so critical for the development of optimum wet strength values as the drying temperature for the given time This is illustrated by the following table:

Table X [10% size prepared with 3% glyoXaL] Drying Wet Strengths Temp. Time Rub Tensile 0. Sec.

I 10% sizeprepared with 4%glyoxall Drying Wet Strengths Temp. Time Rub Tensile As a further example of practice, oxidized starch has been cooked with 5 per cent of glyoxal, under the conditions given above, and then diluted and cooled to the proper consistency (ratio of 1200 grams of starch to about 10 liters of water) and then another 5 per cent of glyoxal was added. When this was used as a sizing solution for paper, upon drying and heating as above, corresponding wet strength and wet rub values were obtained, and also the paper was non-ex- I pandin'g or dimension fast useful for printed maps and other employments where this quality is of primary importance, in that its dimensions were not changed upon wetting, or by successive wetting and drying, within wide ranges of procedures. It appears that this excess glyoxal reacts with the cellulose fibers of the paper itself in some fashion to change their behavior with respect to water, either by making them less subject to the imbibition of water or by causing a tie between the fibers at points of contact. If the residual quantity of unreacted glyoxal, at the end of the drying, causes oxidation-reduction action, it may be removed by leaching.

When penetration resistance to ink, for example, is not of importance, the starch-glyoxal size may be added to the pulp,a waterleaf sheet formed, and this sheet dried and heated as described above. Therewith a paper toweling, for example, may be made which has the stated high increment of wet strengths, and also has improved dry strength values, such as:

Table XI 1 Dry tensile, grams Control experiment (low rosin size) 3297 Oxidized starch size (3% cone.) 3543 Oxidized starch-glyoxal size (10% starch:

3% glyoxal); 5810 and characterized inh aving a sizing predom inantly consisting of reaction product of glyoxal and paper-fmaker smodified starch, said glyoxal being present as one-fiftieth to one-twentieth by weight of the dry weight of starch. A

2. A paper having a wet tensile strength above 1200grams, a wet rub value above 10, and characterized in'having a sizing predominantly consisting of the baked reaction product of papermakers modifiedstarch with one-fiftieth to onetwentieth its weight of glyoxal on the basis of dry weight of starch.

'3; The method of sizing paper, which comprises applying to the fibers a water dispersion of a 5 to 9 35 per cent of paper-makers modified starch reacted with 2 to per cent of glyoxal on the basis of the dry weight of starch, drying the water from the paper, and thereafter heating to a temperature of 110 C. to 150 C.

4. The method of sizing paper, which comprises heating a paper-makers modified starch and glyoxal in water, the starch concentration being from 5 to 35 per cent and the amount of glyoxal being 2 to 5 per cent by dry weight of starch, applying the sizing liquor to the paper, drying, and then heating to a temperature of 110 C. to 150 C.

5. The method of preparing a sizing liquor for paper, which comprises suspending a papermakers modified starch in water, cooking for about ten minutes at above the gelation point of the starch for effecting swelling of the starch, adding 2 to 5 per cent of glyoxal based on the dry weight of the starch and adjusting the pH value to between 4 and 9, continuing the cooking for about five minutes, and then diluting and cooling the product.

6. The method of preparing a sizing liquor for paper, which comprises cooking a papermakers modified starch in water for about five minutes at about 85 C. for effecting swelling of the starch, and in the presence of about 3 per cent of glyoxal, based on the dry weight of the starch, while maintaining the pH of the liquor between 4 and 9, and then diluting with water and thereby cooling the product to below 70 C.

7. The method of preparing a sizing liquor for paper, which comprises dispersing a papermakers modified starch in water at a concentration of 5 to 35 per cent, dissolving commercial glyoxal in water and adjusting to a pH value of 4 to 9 by weak alkaline salt, adding the glyoxal solution to the starch dispersion and heating at a temperature of about 85 C. for about five minutes, the quantity of glyoxal being about 3 per cent based on the dry weight of the starch, and then diluting and cooling the product to below 70 C.

8. A sizing liquor for paper, comprising water and dispersed therein the reaction product of cooking at 80 C. to 85 C. for about five minutes a 5 to 35 per cent dispersion of a paper-maker's modified starch with 2 to 5 per cent of glyoxal based on the dry weight of starch.

9. A tub-sizing liquor for paper, consisting of water and dispersed therein the reaction product of cooking at 80 C. to 85 C. for about five minutes a water dispersion of about 10 per cent paper-makers modified starch with about 4 per cent of glyoxal based on the dry weight of starch.

of glyoxal based on the dry weight of the starch,

and alsocontaining in addition about 5 per cent of glyoxal.

11 A paper having a wet tensile strength in excess of 900 grams and a wet rub value above 5, and characterized in having a sizing coating thereon predominantly consisting of a reaction product of glyoxal and paper-makers modified starch, said glyoxal being present as one-fiftieth to one-twentieth by weight of the dry weight of starch.

12. The method of sizing paper, which comprises dispersing a paper-makers modified starch in water at a concentration of 5 to 35 per cent, dissolving commercial glyoxal in water and adjusting to a pH value of 4 to 9 by weak alkaline salt, adding the glyoxal solution to the starch dispersion and heating at a temperature of about degrees C. for about five minutes, the quantity of glyoxal being about 3 per cent based on the dry weight of the starch, diluting and cooling the product to below 70 degrees C., applying the sizing liquor to the paper, drying, and then heating to a temperature of degrees C. to degrees C.

13. A sized paper made in accordance with claim 12, and characterized in having a wet tensile strength in excess of 900 grams and a Wet rub value above 5.

' PAUL B. DAVIDSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,106,164 Bowlby Jan. 25, 1938 2,222,873 Leach Nov. 26, 1940 2,258,741 Champion et a1. Oct. 14, 1941 2,354,662 Bryce Aug. 1, 1944 2,370,266 Smith et al Feb. 27, 1945 2,391,621 Powell et a1. Dec. 25, 1945 2,396,937 Bauer et a1 Mar. 19, 1946 2,411,989 Dunham Dec. 3, 1946 2,412,832 Pfeffer et a1 Dec. 17, 1946 2,413,463 Nichols et al. Dec. 31, 1946 2,414,858 Davidson Jan. 28, 1947 2,422,423 Kvalnes June 17, 1947 

1. A PAPER HAVING A WET TENSILE STRENGTH IN EXCESS OF 900 GRAMS AND A WET RUB VALUE ABOVE 5, AND CHARACTERIZED IN HAVING A STRING PREDOMINANTLY CONSISTING OF REACTION PRODUCT OF GLYOXAL AND PAPER-MAKER''S MODIFIED STARCH, SAID GLYOXAL BEING PRESENT AS ONE-FIFTIETH TO ONE-TWENTIETH BY WEIGHT OF THE DRY WEIGHT OF STARCH. 